Feline Infectious Peritonitis: Risk Factors, Symptoms & Treatment of FIP in Cats

Feline infectious peritonitis, also known as FIP, is a rare and often fatal disease. Because many cats carry the virus that causes FIP in cats, it's important to know about this disease if you're a cat parent.

What Is Feline Infectious Peritonitis?

FIP is caused by a mutation of a coronavirus, a kind of virus that many cats carry though it rarely makes them sick. If the coronavirus your cat carries mutates, however, it can cause FIP. Fortunately, mutations rarely occur and the incidence of FIP is low.

The regular coronavirus lives in a cat's gut and is shed in their feces. Cats become infected with it if they accidentally ingest the virus. If the virus mutates into the form that causes FIP, however, it moves from the gut to the white blood cells and is no longer contagious.

Scientists aren't sure what causes the virus to mutate into a lethal form, but some believe that it has to do with a cat's specific immune system response. Additionally, it is not believed to be a zoonotic virus, meaning that it is not infectious to humans.

It is worth noting that this is not the same coronavirus that is linked to the COVID-19 pandemic. Coronaviruses actually have many different strains, and they get their name from the fact that they are surrounded by a halo called a corona.

Risk Factors

Cats with weakened immune systems are at higher risk of developing FIP. This includes cats younger than 2 years old and cats with compromised immune systems — such as cats with herpes and cats who are sick from other viruses. The disease is much more common in households with multiple cats, in shelters and in breeding colonies. Purebred cats also appear to be at increased risk of FIP.

Signs & Symptoms of Feline Infectious Peritonitis

There are two forms of FIP in cats — the wet form and the dry form. Both share the following signs:

• Weight loss
• Loss of appetite
• Tiredness
• A recurrent fever that doesn't go away with antibiotics

The wet form of FIP causes fluid to build up in either the chest or abdomen, resulting in a distended belly and/or difficulty breathing. The dry form can cause vision-related or neurological problems, such as changes in behavior and seizures.

If your cat displays any of the signs of FIP, schedule an appointment with your veterinarian as soon as possible so they can evaluate your cat. Since some infectious diseases may cause the same signs as FIP, it's also a good idea to isolate your cat from any other pets in your household and to keep them inside until the vet sees them.

Diagnosis and Treatment of FIP in Cats

Unfortunately, FIP is tricky to diagnose. Most vets use a combination of exam findings, the cat's health history and lab tests to diagnose FIP. In veterinary hospitals, there are no routine lab tests that doctors can run to specifically diagnose FIP. However, if the vet takes samples of fluid from your cat's chest or abdomen, they can send them to a special laboratory to be tested for FIP viral particles.

Currently, there's no mainstream treatment or cure for FIP. Most vets consider the disease to be fatal. Research in the Journal of Feline Medicine and Surgery, however, shows the extremely promising treatment of FIP with nucleoside analogs, a new antiviral drug treatment. Further studies are needed to assess the safety and efficacy of this treatment.

How to Prevent FIP in Cats

Because having a strong immune system protects cats from FIP, the best way you can help prevent the disease is by supporting their immune system. This includes:

• Feeding them a complete and balanced cat food
• Providing them with daily exercise and mental stimulation
• Taking them to the vet for regular checkups, vaccinations and deworming
• Addressing any disease early on — including obesity and dental disease
• If you have multiple cats, avoiding overcrowding by providing each cat with a minimum of 18 square feet and their own food and water bowls, litter boxes, toys and resting places
• Keeping food and water bowls away from the litter box
• Keeping your cat indoors only, or only letting them out on a leash or in an outdoor enclosure, like a catio.